Impeller For Centrifugal Blasting Wheel

ABSTRACT

An impeller for a centrifugal blasting wheel includes a base plate, a support collar, and a plurality of spaced rotor blades interconnecting the base plate and support collar. A step is formed at the inner end of the collar and the outer ends of the rotor blades which causes blasting shot to be discharged to the throwing blades of the blasting wheel in a relatively more radial direction to reduce wear of the throwing blades. The base plate also has a frustum-shaped central boss formed to minimize wear of the base plate by the blasting shot. The frustum-shaped central boss has a recess formed therein so that the head of the bolt that connects the impeller to the throwing wheel is located entirely within the recess to also reduce wear of the bolt head.

BACKGROUND OF THE INVENTION

The present invention relates to centrifugal throwing wheels, sometimesreferred to as centrifugal blasting wheels or centrifugal shotblastwheels, used to project streams of abrasive particles against aworkpiece to subject the surface of the workpiece to cleaning orabrading action. More specifically, the present invention relates to animpeller for the blasting wheel which is used to feed and distribute theabrasive particles to rotating blades of the blasting wheel.

Installations equipped with centrifugal blasting wheels are typicallyused to remove scale or rust from the surface of metallic workpieces, orto clean the surface of metal castings. Centrifugal blasting wheels willtypically employ a throwing wheel assembly having a plurality ofradially extending throwing blades mounted on a rotatable wheel. Thethrowing blades are positioned to receive a stream of abrasiveparticulate material, sometimes referred to as blasting shot, and thenthrow the particulate material radially outwardly from the wheel at anappropriate discharge location. A rotary impeller is used to receive theblasting shot from a feed spout, and distribute the blasting shot to therotating throwing blades.

In a centrifugal throwing wheel of this type, sometimes referred to asan airless centrifugal throwing wheel, not all of the abrasive particlesof blasting shot move radially outwardly from the impeller in adirection that is preferably tangential to, and as parallel as possibleto, the surfaces of the throwing blades when they emerge from theopenings in the distributing impeller. A considerable number of theabrasive blasting shot particles strike against the edges of theopenings in the impeller, as well as other surfaces of the impeller, tocause the blasting shot to deflect or bounce back and forth, orreverberate in a ping-pong like manner, within the area housing therotating throwing blades. Such action not only reduces the exit speed ofthe blasting shot, but also causes the blasting shot to be non-uniformlydistributed over the surface of the workpiece being processed. Further,such action also increases the degree of wear on the impeller, thethrowing blades, and other components of the centrifugal throwing wheelthat are subject to contact with the blasting shot particles.

It is therefore an object of the present invention to reduce the degreeof wear caused to components, such as the impeller and throwing blades,of a centrifugal blasting wheel by the abrasive blasting shot.

Another object of the present invention is to improve the directionalflow of the abrasive blasting shot as it exits the impeller to providemore efficient cleaning and abrading action for the centrifugal blastingwheel.

SUMMARY OF THE INVENTION

The present invention provides an impeller for feeding blasting shot tothrowing blades of a centrifugal blasting wheel. The impeller receivesblasting shot from a feed spout, and distributes or discharges at leastsome of the blasting shot in a relatively more radial direction to therotating throwing blades. The result is more of the blasting shotexiting the impeller in the desired radial direction, and a reduction ofthe disadvantages discussed above with respect to prior impellers usedwith centrifugal blasting wheels.

In one aspect, there is provided an improved impeller for a centrifugalblasting machine comprising: (a) a base plate adapted for rotation abouta central axis of rotation, the base plate extending substantiallyperpendicularly from the axis of rotation, and having an outercircumferential end radially spaced from the axis of rotation; (b) acollar axially spaced from the base plate and circumferentiallysurrounding the axis of rotation, the collar defining an interiorcircumferential surface and an exterior circumferential surface; (c) aplurality of axially extending and circumferentially spaced apart rotorblades connecting the outer circumferential end of the base plate andthe collar to thereby define a generally cylindrically shaped interiorspace and a plurality of axially and circumferentially extendingopenings therebetween to permit discharging of blasting shottherethrough from the interior space upon rotation, and each of therotor blades defining an inner circumferential surface and an outercircumferential surface; and (d) the outer circumferential surfaces ofthe rotor blades being located radially inward of the exteriorcircumferential surface of the collar to define a step for deflectingblasting shot exiting the interior space in a relatively more radialdirection.

In another aspect of the invention, the step is concavely-shaped. Theconcave shape is preferably shaped as an arc of a circle having a radiusof from about 2 inches to about 6 inches, more preferably shaped as anarc of a circle having a radius of from about 3 inches to about 5inches, and most preferably shaped as an arc of a circle having a radiusof about 4.25 inches. This concavely-shaped surface improves thedirectional flow of the blasting shot by deflecting more of the blastingshot in a radial direction rather than in random directions.

In yet another aspect of the invention, the base plate has an annularinner surface facing the interior space of the impeller which surroundsa frustum-shaped central boss projecting axially into the interiorspace. A bolt-receiving opening is formed through the central boss, andextends co-axially with the axis of rotation. The bolt-receiving openinghas an annular recess formed therein for engaging a bolt head. The axialdepth of the recess is such that the head of the bolt is locatedentirely within the recess so as to minimize wear of the bolt headduring operation of the centrifugal blasting wheel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional side view in elevation of a centrifugal blastingwheel incorporating an impeller of the present invention;

FIG. 2 is an end view of the impeller looking into the interior thereofalong its axis of rotation;

FIG. 3 is a side view of the impeller; and

FIG. 4 is a sectional view of the impeller.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 illustrates a centrifugal blasting wheel assembly, generallydesignated by the number 10, incorporating an impeller 12 constructed inaccordance with the present invention. The blasting wheel assembly 10includes a throwing wheel 14 having an axis of rotation 16, and which isdriven by a motor and drive shaft (not shown) via bolt 18. A hub 20 isaffixed to throwing wheel 14 for rotation therewith, and impeller 12 inturn is centrally mounted to hub 20 for rotation with hub 20 andthrowing wheel 14. A plurality of rotating throwing blades 22 areremovably mounted on, and are generally perpendicular to, the inner face24 of throwing wheel 14.

The impeller 12 receives a stream of abrasive particulate blastingmaterial, typically referred to as blasting shot, from a feed spout 26,and in turn feeds the blasting shot to the throwing blades 22. Theimpeller 12 is provided with a plurality of openings 28, hereinafter tobe more fully described, for delivering the blasting shot through adischarge slot 30 provided in a stationary control cage 32 thatsurrounds the impeller 12 and in which the impeller 12 rotates. Theblasting shot is thereby received at the inlet ends of the throwingblades 22 as the blades 22 rotate past the discharge slot 30 of controlcage 32. The blasting shot is then accelerated as it moves radiallyoutwardly along the surface of the throwing blades 22 until it is thrownfrom the distal end of the blades 22 at a desired discharge pointagainst the surface of a workpiece.

Turning now to FIGS. 2-4, the impeller 12 is illustrated in more detail.Impeller 12 includes a base plate 34 that extends substantiallyperpendicularly to the axis of rotation 16. Base plate 34 has an outersurface 36 that abuts against hub 20, and is mounted to hub 20 by bolt18 for rotation therewith. Base plate 34 also has an annular innersurface 38 facing the interior of impeller 12, and as shown best in FIG.4, the annular inner surface 38 surrounds a frustum-shaped central boss40 that projects axially into the interior of impeller 12. As shown bestin FIG. 4, the frustum-shaped central boss 40 includes an annular wallsloping axially inwardly from the annular inner surface 38 at an angle Awith respect to the annular surface 38. Angle A is preferably betweenabout 2 degrees to about 15 degrees, more preferably between about 5degrees to about 12 degrees, and most preferably about 10 degrees. Suchangles minimize the amount of interference between the boss 40 and theblasting shot resulting in less wear of the base plate 34.

The frustum-shaped central boss 40 has a bolt-receiving opening 42formed axially therethrough, and which extends co-axially with the axisof rotation 16. As best shown in FIGS. 1 and 4, the bolt-receivingopening 42 includes an annular recess 44 formed therein for receivingthe head of bolt 18 and engaging against the underside of the head ofbolt 18 when bolt 18 is turned to tighten impeller against hub 20.Recess 44 thus forms a circular ridge or edge 46 along the apex offrustum-shaped central boss 40, and has an axial depth such that theentire head of bolt 18 lies within recess 44 when the underside of thehead of bolt 18 engages recess 44 so that bolt 18 is completely seatedtherein. Preferably, the outerside of the head of bolt 18 is flush withor slightly beneath the circular ridge or edge 46 formed by the apex ofboss 40. Positioning the outerside of the head of bolt 18 to be flushwith or slightly beneath the apex of boss 40 substantially reducesinterference between the head of bolt 18 and the blasting shot withinthe interior of impeller 12, and thus substantially reduces wear of thehead of bolt 18 during operation of centrifugal blasting wheel 10.

As shown best in FIGS. 3 and 4, impeller 12 also includes a collar orsupport ring 48 axially spaced from base plate 34. Collar 48 surroundsaxis of rotation 16, and includes an interior circumferential surface 50and an exterior circumferential surface 52. As shown best in FIG. 4,interior circumferential surface 50 tapers outwardly towards the openend of impeller 12. In other words, the axially outer end of surface 50,i.e. the end of collar 48 that is closest to feed spout 26, as seen inFIG. 1, is located radially at a greater distance from axis of rotation16 than is the axially inner end of surface 50, i.e. the end of collar48 that is furthest from spout 26, as seen in FIG. 1. This taper ofinterior surface 50 helps to prevent the outer end of collar 48 frominterfering with the feed spout 26, and helps to direct blasting shotinto the interior of impeller 12.

As shown best in FIG. 3, impeller 12 further includes a plurality ofaxially extending and circumferentially spaced apart rotor blades 54which connect the outer circumferential end of base plate 34 and theaxially inner end of collar 48. Each rotor blade 54 defines an innercircumferential surface 56, which faces the interior of impeller 12, andan outer circumferential surface 58, which faces the exterior ofimpeller 12. The base plate 34, collar 48 and interconnecting rotorblades 54 thus form a generally cylindrically shaped interior space aswell as the plurality of axially and circumferentially extendingopenings 28 located between each of rotor blades 54. As shown in FIG. 3,openings 28 and rotor blades 54 are substantially rectangular in shape,and have an axial length that is about twice their circumferentialwidth. As previously described herein, openings 28 permit the dischargeof blasting shot therethrough from the interior space of impeller 12 tothrowing blades 22 upon rotation of impeller 12.

As shown best in FIG. 4, the outer circumferential surface 58 of rotorblades 54 are disposed radially inwardly of the exterior surface 52 ofcollar 48 to define a step 60 that extends circumferentially around theentire inner end of collar 48. Step 60 is concavely-shaped, and ispreferably shaped as an arc of a circle having a radius of from about 2inches to about 6 inches, more preferably as an arc of a circle having aradius of from about 3 inches to about 5 inches, and most preferably isan arc of a circle having a radius of about 4.25 inches. The radius (R)is determined by the conventional formula: R=H/2+W²/8H where W is thewidth or straight line distance of the arc between its beginning pointand its ending point, and H is the height of the arc from the straightline drawn between the beginning and ending points of the arc and theapex of the arc.

During operation of the centrifugal blasting wheel 10, some of theblasting shot exiting the interior of impeller 12 through openings 28engages step 60. Due to its position and shape, step 60 causes theblasting shot to deflect in a relatively more radial direction, ratherthan in random directions, through the discharge slot 30 in control cage32 to thereafter be picked up by throwing blades 22. The exit speed ofthe blasting shot at the distal ends of the throwing blades 22 isthereby increased, the blasting shot is more uniformly distributed tothe surface of the workpiece, and wear of the throwing blades 22 isreduced due to less violent contact or collisions between the blastingshot and the surfaces of the blades 22.

1. An impeller for feeding blasting shot to a centrifugal blastingwheel, comprising: (a) a base plate adapted for rotation about a centralaxis of rotation, said base plate extending substantiallyperpendicularly from said axis of rotation, and having an outercircumferential end radially spaced from said axis of rotation; (b) acollar axially spaced from sais base plate and circumferentiallysurrounding said axis of rotation, said collar defining an interiorcircumferential surface and an exterior circumferential surface; (c) aplurality of axially extending and circumferentially spaced apart rotorblades connecting the outer circumferential end of said base plate andsaid collar to thereby define a general cylindrically shaped interiorspace and a plurality of axially and circumferentially extendingopenings therebetween to permit discharging of blasting shottherethrough from said interior space upon rotation, and each of saidrotor blades defining an inner circumferential surface and an outercircumferential surface; and (d) a step for deflecting blasting shotexiting said interior space in a relatively more radial direction, saidstep defined by the outer circumferential surfaces of said rotor bladesbeing disposed radially inwardly of the exterior circumferential surfaceof said collar.
 2. The impeller of claim 1 wherein said step isconcavely-shaped.
 3. The impeller of claim 2 wherein said step is an arcof a circle having a radius of from about 2 inches to about 6 inches. 4.The impeller of claim 2 wherein said step is an arc of a circle having aradius of from about 3 inches to about 5 inches.
 5. The impeller ofclaim 2 wherein said step is an arc of a circle having a radius of about4.25 inches.
 6. The impeller of claim 1 wherein said base plate has anannular inner surface facing said interior space, and said annular innersurface surrounds a frustum-shaped central boss which projects axiallyinto said interior space.
 7. The impeller of claim 6 wherein thefrustum-shaped central boss of said base plate has an axially extendingbolt-receiving opening formed therethrough.
 8. The impeller of claim 7wherein said bolt-receiving opening includes an annular recess forengaging a bolt head.
 9. The impeller of claim 8 wherein said annularrecess has an axial depth such that the bolt head is located entirelywithin the recess.
 10. The impeller of claim 6 wherein saidfrustum-shaped central boss includes an annular wall sloping axiallyinwardly from said annular inner surface at an angle of from about 2degrees to about 15 degrees with respect to said annular inner surface.11. The impeller of claim 6 wherein said frustum-shaped central bossincludes an annular wall sloping axially inwardly from said annularinner surface at an angle of from about 5 degrees to about 12 degreeswith respect to said annular inner surface.
 12. The impeller of claim 6wherein said frustum-shaped central boss includes an annular wallsloping axially inwardly from said annular inner surface at an angle ofabout 10 degrees with respect to said annular inner surface.